Yep, trailer brakes would be nice, but you'll also have to worry about your tranny. Don't use OD and don't push it too much. I pulled my bronco on a similar setup in a V8 explorer for a 5hr round trip, but it was over a course of a weekend (2 2.5hr trips). I also pulled my bronco 2hrs up steep grades in Colorado with the same setup. It was less than ideal and probably not good at all on the tranny, but it survived. Try not to make the tranny shift much and take it easy, you'll probably be fine. If you plan to do this often, I'd look into a tranny cooler. Oh, you should load the bronco on the trailer so that the rear of your Navigator squats a couple inches. It's a delicate balance between overloading your truck and centering the weight on the trailer. Weight centered on the trailer makes the trailer fishtail bcause it jerks around the rear of your tow rig with any slight steering.
J.D.